584 



THE NERVOUS SYSTEM 



It has already been shown that the motor fibers of the internal capsule of 

 one side cross over to the opposite side in the decussation of the pyramids in 

 the medulla. This decussation is not quite complete, as some fibers pass 

 down on the same side in the direct pyramidal tract. A small portion of these 

 direct fibers end around the motor neurones of the same side, but the great 

 majority cross to the opposite side in the anterior commissure at some lower 

 level of the cord. It follows that the motor areas of the cortex on one side 

 control the muscular movements of the opposite side of the body, but to a slight 

 extent those of the same side. Disease in the region of the fissure of Rolando 

 is usually accompanied by a disturbance of the motor function on the opposite 

 side of the body, although there is some slight motor disturbance on the same 

 side. 



LOCALIZATION OF SENSORY FUNCTION IN THE CEREBRAL 



CORTEX. 



There is evidence that fibers from the nerves of special sense are specially 

 connected with definite and distinct parts of the cerebral cortex. 



The fibers from the sensory nerves, we have found, are connected with the 

 cerebral cortex by a chain of neurones. . These sensory paths, although com- 

 plex, are definite and distinct. Their cortical connections have been mapped 

 out with considerable definiteness. 



The Body Sensory or Somesthetic Area. The motor function around 

 the fissure of Rolando for a long time obscured the fact that this region, 



FIG. 415- Diagrams to Show Flechsig's Sensory and Association Areas ont e Surface of the 

 Cerebral Hemisphere. (From Cunningham, after Flechsig.) 



especially the post-central convolution, is intimately connected with the 

 perception of general body sensations. Physiological and pathological ob- 

 servations supported this view, and recently Flechsig has much strengthened 

 the view by his method of studying the progressive development of the brain. 

 In figure 415 we produce Flechsig's diagram showing the body sensory (som- 

 esthetic) area. The borders of the area are more or less indefinite and less 



